"budo karate of Mas Oyama" By Cameron Quinn. But it is out of print.
"Oyama: The Legend, the Legacy" by Michael L. Lorden. It has a few glaring mistakes (such as listing a shotokan legend as a kyokushin personality), but it is easy to find.
"The Kyokushin Way" by Mas Oyama.
I can give good books for shinkyokushin and several of the other factions. But I have no clue how NAKO kihon variations goes or if the books would be of use to you.
I can give good books for shinkyokushin and several of the other factions. But I have no clue how NAKO kata variations goes or if the books would be of use to you.
Good books on kumite are rare in english. You got much more choice in Japanese.
Actually, I would recommend DVDs.
Howard Collins "kyokushin knockdown karate handbook" is good, but VERY out of print and hard to find.
You could try "Sabaki method: karate in the inner circle" by Joko Ninomiya -its Enshin karate, not kyokushin. But its very good knockdown kumite tutorial (if you dont use the stuff banned in kyokushin such as grabbing).
Same thing with "perfect karate" by Shigeru Oyama. Very good, but not entirely according to kyokushin sport knockdown rules.
Kakatootoshi have kindly mentioned a few others in a few similar threads.
There are also book versions to accompany the shinkyokushin "born to be the strongest" DVD serie on kumite techniques. But I cannot find their names or links to them mentioned in the forum (I know they have been mentioned here. By Kakatootoshi if I remember right)
For kata and kihon, you could take a look at "Kyokushin karate" (also released as Power karate vol1&") by David C. Cook. It is very outdated for any group so dont rely on it for grading purposes, but it very good. It is out of print but has been rreleased by Cook on his own styles webpage: http://www.tsg-international.com/powerkarate/
You could also go for any and all of Mas Oyamas books. But they are all technically dated compared to how any group do techniques now. Very nice read, and lot of good tips and inspiration, but you need to know that they are old.